Author: Miguel A. Ballicora
Date: 16:14:49 09/25/01
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On September 25, 2001 at 18:36:57, Bruce Moreland wrote: >On September 25, 2001 at 10:29:56, Robert Hyatt wrote: > >>I don't see this as a problem. The issue still remains, "can you do something >>parallel that executes more than 2x faster than what you do serially?" If the >>answer is "yes" then there is something basically wrong with your serial >>algorithm... > >If I make a minor change to my program, the same search might take half as long, >or twice as long, or whatever. > >If I run a given search serially, with a particular version, it takes X time. > >If I run the same search with a two-processor parallel version, it might take >1/2X time, or 1/4X time, or X time, or even >X time. I believe this happens for >the same reason that when I make a minor change to my serial version, I get >different search times. > >If I could consistently get less than 1/2X time with two processors, that'd be >something to be happy about, and it would also raise some serious questions, >obviously. > >But I don't think it is necessarily true that this would violate the laws of >physics. > >If the two halves of the problem were absolutely independent, then of course, >you'd have a 2X speedup at best. > >Since there is interaction between the two threads, it is not necessarily true >that you can have at most a 2X speedup. It is possible to construct a >hypothetical case where one thread helps the other to over-achieve, and perhaps >there are problem domains where these hypothetical cases would be the rule, >rather than the exception. > >Chess programs are deeply flawed from the start, so I'd believe that anything >might be *seen*. Whether it's seen for a reason, or due to random chance, I >don't know. > >But I don't think that people who argue for super-scalar speedups are >necessarily arguing in favor of perpetual motion machines. > >bruce I agree. In science those kind of phenomena are called synergistic effects. It is like iterative deepening, if you do not know it, it might sound crazy that it is faster than going directly to ply = x. Of course, it is obvious when you understand it... but... how many things are they that we do not understand yet? I do not see any theoretical constraint. Regards, Miguel
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